1. Field of the Invention
The present invention relates to a developer transferring device comprising an agitating transfer member for transferring a developer containing a toner and a magnetic carrier in an axial direction while agitating the developer as it rotates, and toner concentration detecting means for detecting the toner concentration of the developer that is transferred by the agitating transfer member. The present invention also relates to a developing device, a process unit, and an image forming apparatus using the developer transferring device.
2. Description of the Related Art
Conventionally, this type of developing device carries a developer transferred by an agitating transfer member such as a screw member to the surface of a developer carrier such as a developing sleeve, and transfers the developer to a region facing an image carrier in accordance with the surface movement of the developer carrier. Then, by transferring the toner contained in the developer to a latent image on the image carrier, the latent image is developed, and a toner image is obtained. The developer used in the developing process is returned to the agitating transfer member in the developing device in accordance with the surface movement of the developer carrier, whereupon the toner concentration is detected by toner concentration detecting means as the developer is transferred by the agitating transfer member. Then, on the basis of the detection result, an appropriate amount of toner is added, whereupon the developer is supplied to the developer carrier again.
In a developing device constituted in this manner, when the volume of toner in the developer varies due to environmental variation and variation in the toner charge, the detection result produced by the toner concentration detecting means varies regardless of whether the toner concentration is constant or not, and as a result, a detection error occurs. Such detection errors can be suppressed by pushing the developer forcibly into a detection position of the toner concentration detecting means such that the toner volume is appropriate for the toner concentration.
FIG. 10 of Japanese Unexamined Patent Application Publication H6-308833, for example, is a graph illustrating that a constant detection result can be obtained by a permeability sensor serving as the toner concentration detecting means, regardless of the toner charge, by pressurizing the developer to a force of 30 [g/cm2] (9.8×300N/cm2) or more.
However, in an experiment performed by the present inventors, it was found that in actuality, the permeability sensor does not always exhibit the output characteristics shown in the graph. More specifically, the developing device described in Japanese Unexamined Patent Application Publication H6-308833 transfers the developer in a rotary axis direction in accordance with the rotation of a screw member serving as an agitating transfer member, which is disposed in a developer transfer portion. The toner concentration of the transferred developer is then detected by the toner concentration detecting means, which are fixed to a lower wall of the developer transfer portion. On a downstream side of a toner concentration detection position of the toner concentration detecting means in the developer transfer direction, surface roughening processing is implemented on an inner wall of the developer transfer portion. Then, by reducing the developer transfer speed in the location of the surface roughening processing, the developer in a toner concentration detection position on the upstream side thereof in the developer transfer direction is pressurized in the developer transfer direction. However, according to the experiment performed by the present inventors, with this constitution, a favorable correlation is not exhibited between the pressurizing force applied to the developer in the developer transfer direction and the detection result produced by the permeability sensor serving as the toner concentration detection sensor.
Hence, after performing another experiment, the present inventors found that the reason for being unable to obtain a favorable correlation between the pressurizing force applied to the developer in the developer transfer direction and the detection result produced by the toner concentration detection sensor is as follows. A certain degree of clearance is provided between the wall of the developer transfer portion enveloping the screw member and the screw vane of the screw member. The toner concentration detection sensor fixed to the wall of the developer transfer portion has a comparatively small detectable distance range, and cannot therefore detect the toner concentration of the developer in the part of the screw vane positioned at a comparatively large remove therefrom. In other words, only the toner concentration of the developer in the clearance in the vicinity of the toner concentration detection sensor can be detected by the sensor. Accordingly, the developer in the clearance must be pressurized sufficiently. However, the pressurizing force in the rotary axis direction (transfer direction) accompanying rotation of the screw member acts mainly on the developer stored in the screw vane of the screw member. Therefore, even when the developer in the screw vane is pressurized sufficiently, the developer in the clearance on the outside of the screw vane is not pressurized sufficiently.
As a result, a favorable correlation cannot be obtained between the pressurizing force applied to the developer in the developer transfer direction and the detection result produced by the toner concentration detection sensor.
Meanwhile, Japanese Unexamined Patent Application Publication H5-341649 describes a developing device in which a parallel fin member extending in a parallel direction to the rotary axis direction protrudes from a peripheral surface of a rotary shaft member of a screw member, and a toner concentration sensor is disposed in a region facing the parallel fin member. According to this constitution, the developer is moved in a normal line direction by the parallel fin member and at the same time is pressurized toward the toner concentration sensor. Thus, the toner positioned in the vicinity of a toner concentration detection surface of the sensor is pushed forcibly toward the sensor. As a result, the number of toner concentration detection errors can be reduced in comparison with the developing device described in Japanese Unexamined Patent Application Publication H6-308833.
However, the present inventors discovered through experiment that even with this developing device, the developer in the vicinity of the toner concentration detection sensor cannot be pressurized sufficiently, and therefore detection errors may occur.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Unexamined Patent Application Publication S63-049569, Japanese Unexamined Patent Application Publication S64-038718, Japanese Unexamined Patent Application Publication H11-202610, Japanese Unexamined Patent Application Publication 2003-215903, and Japanese Unexamined Patent Application Publication 2003-307918.